by Jane Harris Zsovan
Twentieth century animal breeders like the Heck brothers tried to recreate extinct species by backbreeding. In the process they created some dubious throwbacks like their reconstituted tarpan. But the hope of recreating extinct species remains.
For example, David Haussler, Professor of Biomolecular Engineering at University of California Santa Cruz, tries to recreate a path of evolution back to a common ancestor via a computer program. He tracks the genetic sequences of mammals, looking for portions of the genome that are identical. The unchanged portions of the genome are assumed to be handed down to us by the common ancestor of all mammals.
But, in a move that leaves human computer simulation in the dust, some life forms can apparently reverse their own evolution. What's really happening here?
Bacteria reverse evolution?
Recently, Daniel Falush and his team at University College Cork, Ireland, reported that two bacteria species that cause food poisoning, Campylobacter coli and C. jejuni, are apparently converging by exchanging their genes. The level of genomic difference suggests that they are separated by about 100 million years, but they are thought to be merging at four times that rate. One problem, however, is that - as the researchers themselves note in their abstract - the boundaries of bacterial species "remain controversial." Conventional definitions of species assume ancestor-descendant relationships, but bacteria can swap their genes, as these two groups are doing. So just how to determine that bacteria are separate species is not as clearcut. Also, what must still be determined, as other researchers have noted, is whether the converged bacterium will be any better at poisoning food than its predecessors.
The threespine stickleback's spiny backtracking
A much more remarkable example of apparent reverse evolution is a little fish in Washington State, U.S.A. The threespine stickleback is named for its bony armour plate. But as Seattle's Lake Washington became highly polluted over the years, the predatory trout population could barely see the sticklebacks. Many threespines got by with relatively little armor plate.
However, when the lake was cleaned up during the mid-twentieth century, trout could see better. The threespine once again developed body armour which made it unpalatable to trout. It dug back into its genetic code to find traits to survive in a changing genetic niche.
The cause of the change is relatively easy to understand. The tastiest sticklebacks were the ones with the fewest spines, and they got eaten as soon as the trout glimpsed them. Of course, that left the spinier sticklebacks, who had continued to exist in much smaller numbers, to reproduce. So, now the lake population has reverted to the spiny design of its salt water ancestors.
The fish's rearmament program, a form of reverse evolution, has created a stir among researchers at the Fred Hutchinson Cancer Research Center who hope that it may have implications for the study of disease in humans. The study, Rapid, Dramatic 'Reverse Evolution' Documented In Tiny Fish Species, was published in the May 20, 2008, issue of Current Biology.
A challenge to Darwinian theory?
Catherine Peishal of the Hutchinson Cancer Center Lab says the findings "established the stickleback as a new model for study of complex genetic traits." She adds that "having a lot of genetic variation in the population means that if the environment changes there may be some gene variant that does better than the previous one, and so nature selects for it. Genetic variation increases the chance of overall survival for a species," she says.
Peishal even suggests that the threespine stickleback's reversion directly challenges one explanation of rapid speciation: phenotype plasticity.
According to this explanation, the environment may cause one animal to express an existing gene differently. After several generations, enough genetic changes may occur that the animal's offspring evolve into a different species. Environment plays the key role in sparking short term adaptations though genetic change takes longer.
But according to Peishal's team, that did not happen to the sticklebac, whose record we now have for some decades. Existing genetic diversity among the Seattle Lake sticklebacks played a larger role than environment in causing rapid physical changes. The stickleback reverted to fuller body armour, an adaptation that was still present in its genes and was once again favoured by circumstances.
In other words, the stickleback did not "evolve" the armoured trait all over again. Greater numbers of sticklebacks were hatched with the existing available trait.
No surprise to ID proponents
Well, the threespine stickleback's "reverse evolution" shouldn't come as much of a surprise to readers of this blog. We've explored the genetic diversity among bovoid, canine, and equine species, and what have we found? Like the stickleback, these species retain a level of genetic diversity over a long period of time that allows them to adapt to often diverse, unexpected, or even hostile niches.
Time and again, animals such as the Canadian Horse and the Carolina Dog recover and draw upon dormant traits to adapt. It is the breadth of the genetic code, rather than either genetic specialization or the development of new traits that helps living creatures survive ecological shifts. And we've seen how, even after millennia of separation, the bison and wisent appear to be able to interbreed, which suggests that successful species do not let go of ancestral traits very readily.
Many successful species possess a diverse gene pool that allows them to adapt over a few generations to a changing environment. Far from readily evolving new traits, their genetic codes retain traits that appear useless. But when circumstances changes, that "genetic baggage" often turns out to aid survival. Is this genetic baggage part of their design?